Thermal and acoustical insulating shields have long been known in the art. Such shields are used in a wide variety of applications, among which are shielding in space crafts, automobiles, home appliances, electronic components, industrial engines, boiler plants and the like. Some of such shields have proportionally smaller thermal insulating value and proportionally higher acoustical insulating value, and vice versa. There are, of course, shields which lie therebetween.
In connection with the thermal insulating value, shields are known which provide thermal insulation, primarily, by virtue of being a radiation thermal shield, while others provide thermal insulation by being, primarily, a conduction thermal shield, and, again, there are shields that lie therebetween. For example, pressed and formed sheet metal has long since been mounted by bolts, nuts, screws, welding, etc. between an object to be protected, i.e. shielded, for example, the floor pan of an automobile, and a heat source, for example, a portion of the exhaust system. Such a formed sheet metal provides thermal insulation, primarily, by re-radiation of heat from the portion of the exhaust system back into the ambient and/or other cooler parts of the undercarriage of an automobile to thermally insulate the floor pan from that portion of the exhaust. Such sheet metal shields, however, have low acoustical insulating value, and a large portion of noise produced in an adjacent portion of an exhaust system can be transmitted through the floor pan of the automobile and into the passenger compartment. Additional noise can be produced by loose shields which vibrate and/or rattle. Such sheet metal shields, also, provides thermal insulation value in connection with conductive heat, since such sheet metal shields will be spaced between the floor pan and the portion of the exhaust, and that spacing provides an air gap between the shield and the floor pan which reduces conductive, and to some extent, convective heat transfer.
Where substantial acoustical shielding is also required, metal shields, as described above, are not satisfactory. In such requirements, the shields generally are at least in part fibrous in nature, e.g. batts of fiberglass, which provide increased acoustical insulation as well as good conduction thermal insulation. However, such insulation can only be used where there are insignificant forces, both static and dynamic, on the fibrous insulation, since batts of fiberglass, for example, have very little strength in any direction, i.e. in either the X, Y or Z directions. Such shields are, however, very useful in certain applications, for example, thermal insulation in domestic dishwashers.
A very particular problem in regard to such shields has been encountered by the automobile industry and like industries, and that problem has become acute in recent years. As the overall size of automobiles continues to shrink, space within any portion of the assembled automobile is now at a premium. For example, in past designs of automobiles, sufficient room existed between the exhaust system of the automobile and the floor tunnel of the automobile that the usual sheet metal shield could be suspended in the tunnel, e.g. with bolts, screws, welding and the like, with specially provided ears or dogs or connectors, so as to space that sheet metal shield from the tunnel and from the exhaust system. This provided a radiation barrier to heat transfer from the exhaust system to the tunnel, as well as a conductive and convective heat transfer barrier in view of the spacing between the shield and the tunnel. This design also provided some acoustical insulation. However, with modern designs, the spacing between the exhaust system and the tunnel is now very much reduced, and in many situations, it is now no longer practical to suspend shields between the exhaust and tunnel, and, moreover, the reduced spacing correspondingly reduces any air gap remaining between the shield and the tunnel, such that very little conductive and convective heat insulation or acoustical insulation results.
As a result of the foregoing difficulty in modern designs, automobile manufacturers have increased the thickness of the material making up the floor covering inside the passenger compartment, i.e. the insulation between the carpet and the floor pan (usually "shoddy" material), so as to decrease the heat transfer from the exhaust system into the passenger compartment. This approach, however, is quite expensive, is fairly labor intensive, and, moreover, still is not satisfactory, in that a passenger, especially where the foot rests, can feel the increased temperature and detect the increased noise. Further, this approach does not shield the exterior of the floor pan, and at higher temperatures of that exterior, the coating thereon will blister and corrosion results.
The art has long recognized that fibrous batts, usually containing inorganic fibers, such as glass fibers, mineral and clay wool fibers, alumina-silicate fibers, silica fibers and the like provide very good thermal and acoustical insulation and could potentially be a replacement for the suspended sheet metal shields. The problem with such insulation is that the batts, especially of such inorganic fibers, are usually made by air laying fibers onto a moving belt, and, hence, the fibers tend to stratify in non-discrete layers throughout the thickness (Z direction) of the batts. Since these fibers are not substantially interlocked in the Z direction, the batt has very low Z-directional tensile strength. Even under static loading of its own weight, for example, a batt of fiberglass will simply sag out of its original configuration when suspended from an upper surface thereof. The art has, therefore, expended substantial effort in attempting to provide greater tensile strength to such fibrous batts, in regard to both the X and Y directions and the Z direction.
An early attempt in this regard is disclosed in U.S. Pat. No. 3,975,565 to Kendall, which proposes a composite structure of layered inorganic fibers and organic fibers which are needled together to provide insulating batts (both thermal and acoustical) which have greater tensile strengths in all directions, especially in the Z direction. In this approach, an inorganic fiber layer, such as that of glass fibers, is sandwiched between two layers of organic fibers, for example, cellulose acetate fibers, and needling of the composite sandwiched layers is achieved from either one or both sides of the composite so as to drive portions of the organic fibers from the organic fiber layer(s) through the inorganic fiber layer (glass fibers) and, thus, to tack the composite together and, particularly, improve the Z-directional strength. However, because of the needling technique used in that process, the needle punch density could not be greater than about 260 needle punches per square inch, since, at above about 260 needle punches per square inch, glass fiber damage resulted and with a more than 25% loss of mat strength. While such an approach certainly improved Z-directional strength, with such low numbers of needle punches, the Z-directional strength of such a composite is still quite low and unacceptable for most modern thermal/acoustical insulating applications where substantial static and dynamic forces are placed on that insulation, e.g. in the suspended use with an automobile, as discussed above.
In U.S. Pat. No. 4,237,180 to Jaskowski, it is proposed to improve such composite thermal and acoustical insulating batts by including in the inorganic fiber layers heat shrinkable organic fibers. After needling, the composite batt is subjected to temperatures sufficient to cause the organic fibers to shrink, e.g. at least 40% in length, whereby the shrinking fibers mechanically interlock the inorganic fibers into a more consolidated form and therefor improves the strength, particularly in the Z direction. However, shrinking fibers is not only a difficult process, but is substantially uncontrollable, and this approach does not result in uniform products. Moreover, the tensile strengths, and particularly the Z-directional tensile strengths, are not greatly improved by that process.
U.S. Pat. No. 4,522,876 to Hiers recognizes the problems noted above and specifically addresses the problem of a low number of needle punches described in the Kendall patent and the undesired results thereof. The Hiers patent takes a different approach in that it achieves high numbers of needle punches per square inch by the technique of ensuring that the barbs of needles passing through an organic fiber outer layer(s) are loaded with the organic fibers of that layer(s) before the barbs reach the adjacent glass fiber layer. Since the barbs are filled with organic fibers, the barbs cannot engage and break the glass fibers as the needles pass through the glass fiber layer, and the resulting batt can be highly needled with exceptional Z-directional strength, as well as greatly improved X- and Y-directional strength. While this approach is a very decided advance in the art, it still encounters difficulties when such batts experience high static and dynamic loadings, such as in the case of an automobile with a suspended shield, as described above. These difficulties will be more clear hereinafter.
A somewhat different approach in the art is described in U.S. Pat. No. 4,851,274 to D'Elia. In that approach, onto a needlable substrate is placed a middle layer of mineral fibers of short lengths such as to preclude interlocking of other fibers of the structure. A top layer of organic fibers is placed thereon. Needling is then achieved through that top layer and middle layer to the substrate with needle punches up to about 3,000 per square inch. Since the inorganic fibers are not substantially interlocked, the web becomes quite flexible and a binder can be applied to that structure, such as a phenolic binder, and set for forming a moldable thermal and acoustical shield useful, for example, as trunk liners. However, the use of a synthetic resin to achieve formability of such a shield is a decided disadvantage, since it is quite expensive to use a binder, and, moreover, the shield must be molded with conventional tools and dies, which themselves are quite expensive.
U.S. Pat. No. 4,996,095 to Behdorf et al attempts to solve the problem by yet a further approach. In that patent, it is proposed that a glass fiber mat be bonded to a sheet of aluminum by an adhesive of a particular nature and that the adhesive-joined composite can be used as a shield between an automobile floorboard and an exhaust system. The composite of the aluminum sheet and glass fiber mat is shaped to the contours of the vehicle by conventional processes, such as deep drawing, combined deep drawing-stretching forming, bending and crimping. The so-formed shield is then applied to the vehicle by a special clamp. While this approach provides a good thermal and acoustical insulation, it still requires conventional forming techniques, as noted above, to configure the shield to the object to be protected and also requires special clamps for affixing the shield to the vehicle. All of this is expensive and time consuming in assembly of the automobile and does not solve the problem or severely limited space in modern designs, as noted above.
As can be appreciated from the above, it would be of particular advantage in the art to provide a thermal and acoustical insulating shield which is flexible, so that it may be manually applied to the vehicle contours, or other structure, without having to be preformed in conventional shaping processes, and which shield is adhesively attachable to the object to be protected and without the need of any mechanical attaching devices, such as clamps, bolts, screws, welds and the like.